This invention relates generally to motorized operators for circuit breakers used on electrical power systems and the like and specifically to electrical operators for such mechanically operated circuit breakers that may be readily installed on site, i.e. in the field.
One of the principal advantages of having the capability of electrically opening and closing circuit breakers is the ability to remotely operate the breaker in response to operator control as well as in response to fault currents. With electrically controlled motorized systems for opening and closing the circuit breakers, load switching and branch circuit protection may be rapidly and effectively accomplished because of the elimination of the need for a technician to physically manipulate the operating mechanism of the circuit breaker.
In many instances, it is desirable to upgrade a mechanically operated breaker by installing a motor control system therefor. Most of the motor control systems include mechanical electric switches to run the bidirectional motor in addition to limit switches for stopping the motor when the breaker reaches an operating position, i.e. either fully opened or fully closed. It is desirable to open or close a breaker rapidly and the limit switches, especially, are difficult and awkward to adjust in the field, and may be adjusted improperly.
As alluded to above, it is desirable that the circuit breaker operate to open or close all electrical phases as rapidly as possible and within a minimum time period for all phases. The motor drive must therefore rapidly start the motor, deliver very high torque for approximately 105 degrees of angular rotation, and rapidly stop. These severe requirements have necessitated the use of expensive apparatus that requires careful adjustment.
The present invention is directed to a novel electronic control system for a bidirectional high torque motor that operates a multiphase circuit breaker through a single reduction gear and a torque limited module. Bidirectional control is achieved by connecting one winding of the motor to the output of a rectifier bridge and connecting the other winding motor in series with the output of the rectifier bridge. The combination is connected in the output of a switching bridge that is controlled by appropriate control signals. The current through the winding connected in series with the rectifier bridge always flows in the same direction, whereas the direction of current flow in the winding coupled to the switching bridge reverses with the different control signals. FET driven transistor switches are used in the switching bridge. A dual monostable timer delivers a timed or predetermined duration of motor drive current, irrespective of the control signal duration and the torque limited module slips to permit the motor to overrun the breaker operation. The motor run time is sufficient to insure that the breaker has been fully operated, that is opened or closed. The torque limited module and the field installable electrical operator are individually the subjects of the above mentioned copending applications since they have separate utility apart from the present invention.